I. Technical Field
The present invention relates to a constant velocity universal joint which is used, for example, in a power transmitting system of automobiles and various industrial machines and which solely allows operating-angle displacement between two shafts on a driving side and a driven side.
II. Description of the Related Art
A fixed type constant velocity universal joint is an example of a constant velocity universal joint used as means for transmitting torque from an engine of an automobile to wheels at constant velocity. The fixed type constant velocity universal joint connects two shafts on the driving side and the driven side and has a structure allowing constant-velocity transmission of rotational torque even when the two shafts form an operating angle. Generally, as in the fixed type constant velocity universal joint described above, a birfield type joint (BJ) and an undercut-free type joint (UJ) are widely known.
For example, the fixed type constant velocity universal joint of the BJ-type includes an outer joint member having a spherical inner surface in which a plurality of track grooves extending in an axial direction are formed equiangularly, an inner joint member having a spherical outer surface in which a plurality of track grooves extending in the axial direction while being paired with the track grooves of the outer joint member are formed equiangularly, a plurality of balls interposed between the track grooves of the outer joint member and the track grooves of the inner joint member so as to transmit torque, and a cage interposed between the spherical inner surface of the outer joint member and the spherical outer surface of the inner joint member so as to retain the balls.
The balls are arranged equiangularly while being accommodated in a plurality of pockets formed in the cage, respectively. In recent years, there is a fixed type constant velocity universal joint that includes eight balls as a fixed type constant velocity universal joint reduced in weight and size.
When the fixed type constant velocity universal joint is used, for example, for a drive shaft of an automobile, there is generally employed a structure in which the outer joint member is connected to a driven shaft, and a drive shaft extending from a plunging type constant velocity universal joint fixed to a differential on the vehicle body side is connected to the inner joint member through spline fit-engagement. In this constant velocity universal joint, when an operating angle is formed between the outer joint member and the inner joint member, each of the balls accommodated in the cage is always maintained within the bisector plane of the operating angle in any operating angle, thereby ensuring the constant velocity property of the joint.
In order to reduce size of the fixed type constant velocity universal joint, it is particularly important to ensure strength of the cage and strength of the inner joint member at the time of formation of a high operating angle.
The conventional constant velocity universal joint disclosed in JP 09-177814 A has a structure in which two kinds of pockets having different peripheral lengths are provided in a peripheral direction of the cage at equal intervals so that sectional areas of poles formed between the pockets and areas of inner and outer spherical surfaces of the cage are increased. In this manner, the strength of the cage is increased.
Further, in the constant velocity universal joint disclosed in JP 2002-13544 A, the shapes of corner round portions of pockets of the cage are regulated by dimension by setting ratio between a radius of curvature R of each corner round portion of the pockets and a diameter d of each ball to R/d≧0.22. In this manner, the strength of the cage is increased.
Further, in the constant velocity universal joint disclosed in JP 3188001 B, the angle of an inlet-side chamfer positioned on a joint-inlet side in a spline hole of the inner joint member is regulated, to thereby increase the strength of the inner joint member.